You can run Despicable Dreadlords

Yes, in this specific deck Leeroy is typically used as a finisher or a quick execute on an enemy minion, Doomguard on the other hand offers a big body and can also be used as a finisher, imo it works fine in this deck.

Cobalt Scalebanes is what if replace, but mirror entity is okay too

Highly disagree with the zoolock and evolve shaman replacement recommendations. In zoolock considering you dont run keleseth youd really want to use the 2 mana cards. Demonfire can create your turn 1 demon ( voidwalker/flame imp) into a big boy in the early game and provides additional removal. You could add a vicious fledgling to the deck and that combined with bloodfury can by itself win you the game sometimes. You should replace the blood imp and fire fly with creepers and fledglings( or techs).
In the evolve shaman argent squire is a really important card since it provides a strong turn 1 Play that can trade into your opponents 1 health minions, and primalfin is just a great card at making tokens and the 3 health make it often hard to remove on your opponents turn ( after you play it) + it has good synergy with flametongue. You usually dont need 2 devolves, but one is a good tech, replace the other one and maybe a jade spirit or chain gang. The 2 blood lusts are a must since you don’t have powerful minions like aya and the pirate package, making a board swarm into blood lust one of your main win conditions. Hope this helps.

Opinions on running 2x Dire Mole instead of the 2x Argent Squire?

Considering its an aggro/tempo based deck, i dont think the mage dk really fits in this, considering when the turn comes when you can use it, youll most likely have to play minions and/or remove your opponents minions/burn his face, the only thing the dk does would be gaining 5 armor and the summon of a 3/6 with lifesteal and a 9 mana 3/6 is pretty bad (even with the lifesteal and armor gain) in a tempo deck. the deck also has no elementals, and considering how late youre gonna be playing it, the hero power most likely wont find a target to kill so you couldnt get another elemental.

On a side note, its worth to try, you could replace the firelands portal with it i suppose.

i decided to use some techs in that spot, breath of sindragosa or arcane missiles for anti aggro and a spellbreaker for big minions taunts when i need to push face damage